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Hierarchical Assembly (hierarchical + assembly)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Templated and Hierarchical Assembly of CdSe/ZnS Quantum Dots,

ADVANCED MATERIALS, Issue 15 2004
Y. Babayan
CdSe/ZnS nanocrystals have been assembled into mesoscale structures (see Figure). Templates with dimensions down to 100,nm are generated via phase-shifting photolithography using composite poly(dimethylsiloxane) masks. Upon removal of the template, the CdSe/ZnS structures are found to exhibit hierarchical order over square nanometers (self-assembly of nanocrystals), square micrometers (template shape), and square centimeters (arrays of template pattern). [source]

Rigid,Flexible Block Molecules Based on a Laterally Extended Aromatic Segment: Hierarchical Assembly into Single Fibers, Flat Ribbons, and Twisted Ribbons

CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2008
Eunji Lee
Abstract Self-assembling rigid,flexible block molecules consisting of a laterally extended aromatic segment and different lengths of hydrophilic coils were synthesized and characterized. The block molecule based on a long poly(ethylene oxide) coil (1), in the melt state, shows an unidentified columnar structure, whereas the molecule with a shorter poly(ethylene oxide) coil (2) self-organizes into an oblique columnar structure. Further decrease in the poly(ethylene oxide) coil length as in the case of 3, on heating, induces a rectangular columnar structure in addition to an oblique columnar mesophase. In diethyl ether, 1 and 2 were observed to self-assemble into uniform nanofibers with bilayer packing. Remarkably, these elementary fibers were observed to further aggregate in a lateral way to form well-defined flat ribbons (1) and twisted ribbons (2) with solvent exchange of diethyl ether into methanol. Furthermore, the ribbons formed in methanol dissociated into elementary fibers in response to the addition of aromatic guest molecules. This transformation between ribbons and single fibers in response to the addition of guest molecules is attributed to the intercalation of aromatic substrates within the rigid segments and subsequent loosening of the aromatic stacking interactions. These results demonstrate that the introduction of a laterally extended aromatic segment into an amphiphilic molecular architecture can lead to the hierarchical formation from elementary fibers of nanoribbons with a tunable twist through controlled lateral interactions between aromatic segments. [source]

In Vitro Formation of Nanocrystalline Carbonate Apatite , A Structural and Morphological Analogue of Atherosclerotic Plaques

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 26 2007
Lars-Fride Olsson
Abstract The in vitro formation of carbonate apatite in solutions with ion concentrations comparable to those in human serum was studied. The composition and morphology of the resulting apatite precipitate displayed a hierarchical assembly of elongated plate-shaped nanocrystals of carbonate apatite analogous to previously characterized bioapatites formed in vivo. The main conclusion is that so-called bioapatites may form in vitro and that precipitation inhibitors most likely are essential for the prevention of spontaneous calcification at normal human serum ion concentrations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

The distribution and kinematics of early high-, peaks in present-day haloes: implications for rare objects and old stellar populations

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005
Jürg Diemand
ABSTRACT We show that the hierarchical assembly of cold dark matter haloes preserves the memory of the initial conditions. Using N -body cosmological simulations, we demonstrate that the present-day spatial distribution and kinematics of objects that formed within early(z, 10) protogalactic systems (old stars, satellite galaxies, globular clusters, massive black holes, etc.) depends mostly on the rarity of the peak of the primordial density field to which they originally belonged. Only for objects forming at lower redshifts does the exact formation site within the progenitor halo (e.g. whether near the centre or in an extended disc) become important. In present-day haloes, material from the rarer early peaks is more centrally concentrated and falls off more steeply with radius compared to the overall mass distribution, has a lower velocity dispersion, moves on more radial orbits, and has a more elongated shape. Population II stars that formed within protogalactic haloes collapsing from ,2.5, fluctuations would follow today an r,3.5 density profile with a half-light radius of 17 kpc and a velocity anisotropy that increases from isotropic in the inner regions to nearly radial at the halo edge. This agrees well with the radial velocity dispersion profile of Galaxy halo stars from the recent work of Battaglia et al. and with the anisotropic orbits of nearby halo stars. [source]